Method of producing a double-walled tube with one of the tubes having integral therewith projecting fin means radially separating the tubes



March 16, 1965 D. F. GRIMM 3,173,196

METHOD OF PRODUCING A DOUBLE WALLED TUBE WITH ONE OF THE TUBES HAVINGINTEGRAL THEREWITH PROJECTING FIN MEANS RADIALLY SEPARATING THE TUBESFiled Nov. 2, 1959 2 Sheets-Sheet l /0 F 5 Z5 226 w /////J mII/IIIIIIIIIII/I March 16, 1965 D. F. GRIMM METHOD OF PRODUCING A DOUBLEWALLED TUBE WITH ONE OF THE TUBES HAVING INTEGRAL THEREWITH PROJECTINGFIN MEANS RADIALLY SEPARATING THE TUBES 2 Sheets-Sheet 2 Filed Nov. 2,1959 INVENTOR.

Unified States Patent 4i 3,173,196 I I l METHOD OF PRODUCING A- DOUBLEWALLED TUBE WITHONEDF TETUBESHAVEWG INTE- GRAL THEREWITH PRQIEC'I'ING FIN MEANS .RADIALLY SEPARATEJG THE TUBES Donald F. Grimm, Southfield,Micln, .assignor, by mesne assignments, to Howard A. From'son, Easton,Conn. FiledNov. Z, 1959, Ser. No. 850,156 11 Claims. (Cl. 29-1573) Thepresent inventio'n relates to a method of producing a double-walled tubehaving a radially separated inner and outer tubes.

One object of the present invention is to provide a new and improvedmethod of making a double-walled tube having radially separated innerand outer tubes.

In accordance with certain aspects of the present invention, one of thetubes is so formed as to define integral therewith radially extendingspacer fins. If the inner tube is-the one provided with the fins, thesefins extend radially outwardly from the outer surface of the inner tube.Where the outer tube is the one provided with the fins, these finsextend radially inwardly from the inner surface of the outer tube; Theinner tube is collapsed, inserted into the outer tube and inflatedoutwardly to form the inner tubular component of the double-walled tube.The inner and outer tubes are so dimensioned, that upon inflation of theinner tube, the fins on one tube come into direct contact with theadjacent surface on the other tube.

Other objects and features of the invention will become apparent as thedescription proceeds, especially when taken in conjunction with theaccompanying drawings, illustrating preferred embodiments of theinvention, wherein:

FIGURE 1 is a fragmentary perspective view of'tubular stock used in thepractice of the present invention.

FIGURE 2 is an end view of the stock shown in FIG- URE 1 after it hasbeen flattened.

FIGURE 3 is an end view of the stock shown in FIGURE 2 after it has beenelongated by rolling.

FIGURE 4 is an end view of reformed tube produced by expanding therolled stock of FIGURE 3.

FIGURE 5 is a view of stock produced by flattening the tubular stock asshown in FIGURE 2, and there after folding the flattened stockpreparatory to rolling.

FIGURE 6 is an end view of the stock shown in FIGURE 4 after it has beenreduced in thickness and elongated by rolling.

FIGURE? is an end view of reformed tubing produced by expanding thestock shown in FIGURE 6.

FIGURE 8 is an end view of stock of the type shown in FIGURE 2 providedwith a double fold.

FIGURE 9 is an end view of the stock shown in FIGURE 8 after it has hasbeen reduced in thickness and elongated by rolling. I

FIGURE 10 is an end view of the partially and completely reformed tubeproduced by expanding the rolled stock of FIGURE 9.

FIGURE 11 is a view of stock produced by simultaneously collapsing andfolding tubular stock of the type shown in FIGURE 1.

FIGURE 12 is an end view of the stock shown in Ice FIGURE 15 is a viewsimiliar to FIGURE '14 showing a double walled tube assembly resultingfrom tubes 'of slightly different fin configuration;

The present invention'relates generally to a; type of tubing produced byfirst providing relatively. thick Walled tubular stock 10 as shown inFIGURE 1.] Stock of this type may be producedby extrusion orotherwise.This tubular stock is first collapsed to produce the fiat stock shown at14 in FIGUREZ whereit will'be' observed that the central cylindricalopening 12 of the stock.-l0' now appears as a closedslit 16. .The,flatstock 14 ofFIG- URE 2 isnow further processed. by passing. itthrough pairs of reducing rolls'tnot shown) which hasthe effect ofreducing the wall thickness of the stock and wire spondingly, elongatingthe stock .to. the. relatively. thin closed tube in the form of aribbon. By ribbon is meant astrip having a Width greater than thethickness indicatedatlS. in FIGURE 3. It willbe observed that theinitial wall 'thickness .of the tubular stock or ribbon of FIGURE 1determines the height of 'fin portions 29 of the rolled strip tubingshown in FIGURE. 3.

Finally, the. rolled strip tubing 18. is reformed into tubing by openingup the closed slit 16 by suitable processes which .form no part of thepresent invention.

However, it will be .noted that the tubing may be-re formed by internalfluid pressure, mandrels, or the like.

A comparison 'of FIGURES'S and 4 .makes vit apparent that the finportions 20 of the flattened strip tubing shown in FIGURE 3 will appearvas radially. outwardly projecting axially extending fins 22 on thereformed or expanded tube 24. i

.The foregoing process and product is at present known and thei'mprovementherein involves an improvement in the finished reformed tuberesiding in the provision of additional radially projecting axiallyextending integral fins, at least two-of which project radiallyoutwardly and one or more of which project radially inwardly. 1 1

.Reference is now made to FIGURES 5-7 illustrating the presentinvention. In this case tubular stock is flattened and folded to producerelatively thick walled stock 26 having a closed slot 28. The stock 26is elongated by rolling tov produce the relatively thin,walled stock-3tlhaving fin forming portions .32, 34, '36. and 38. When the stock 30 ofFIGURE 6 is expanded to formthe tube 4% the. fins 32, 34. and 36 are.radially outwardlyprojecting axially extending fins and the fin 38 is aradially inwardly projecting axially extending fin. Referring now toFIGURES 8-10 the tubular stock is flattened and provided with. a.double:fold to produce the substantially S shape stock-42 of FIGURE 8. Thisstock is reduced in thickness and is elongated by-rolling to form therelativelythin walled stock 44 ofFIGURE 9.

When this rolled stock is reformed into generally tubular shape some ofthe tin forming portions providednby the folding operation will appearat the inside of the tube and some of the fin forming portions willappear at the outside ofthe tube. Specifically,.relatively thick finforming portions 46 and 4-8will .appear at the outside of the reformedtube 50. Relatively thinner fin forming portions52 and 54 will alsoappear at diametrically opposite portions on the outside of -the tube50. The relatively thinner fin forming portions 56 and 58 appear at diametrically opposite portions at the inner surface of the tube 50. t I

Referring now to FIGURES 11 13 there is. illustrated a variation of theforegoing. .In this case relatively thick tubular stock issimultaneously folded and flattened to produce the stock illustrated at60 in FIGURE 11.. It willbe appreciated that stock of this shape may beproduced by forming diametrically opposite lateral portions of tubularstock inwardly to produce the folds or creases 62 while the stock issimultaneously flattened.

After the stock is flattened and folded to the shape shown in FIGURE 11,it is rolled to reduce the wall thickness and to elongate the stock.After rolling the flattened and folded material is in the conditionillustrated at 64 where it will be observed that it includes fin formingportions 65, 66, 67, 68, 69 and '70. In this case it will be observedthat all of the fin forming portions 65, 66, 67, 68, 69 and 70 are ofsubstantially equal thickness. \Vhen the material 64 is reformed intothe tube illustrated at 72 it will be apparent that the fin formingportions 67 and 68 appear at the inside of the tube, whereas the finforming portions 65, 66, 69 and 70 appear at the outside of the tube.

A review of the FIGURES 3-13 indicates that in general, where therolling operation is carried out in such a way as to produce elongationwithout increasing the width of the stock, the thickness of the fins isusually twice the thickness of the tube wall after the material has beenreshaped in tubular form. In some cases, as for example the fins 32 ofFIGURE 7 and the fins 46 and 48 of FIGURE 10, the fin thickness is equalto approximately four times the wall thickness of the finished tube.

Similarly, the height of the tube is approximately equal to the originalwall thickness of the tubular stock prior to the rolling operation.

While the production of round tubes is illustrated herein, it will ofcourse be appreciated that the tubes may be opened up to square, oval,or other non-circular shape.

It will also be understood that the flattened tubes may be partiallyrolled, then folded, and thereafter rolled to final form in foldedcondition.

Referring now to FIGURES 14 and there is illustrated a modifiedconstruction made possible by the use of internally and externallyfinned tubes produced in accordance with the foregoing description.

In FIGURE 14 there is shown a compound tube structure comprising aninner tube 80 and an outer tube 81 in which the inner tube is nested.The inner tube 80 is provided with a single radially inwardly projectingaxially extending fin 82 and three radially outwardly projecting axiallyextending fins 84, 85 and 86. The outer tube 81 is provided with asingle radially inwardly projecting axially extending fin 87 and threeequally spaced radially outwardly projecting axially extending fins 88,89 and 90. It will be recognized that the inner and outer tubes 80 and81 are essentially of the form shown in FIG- URE 7.

The inner and outer tubes are assembled together in such a way that theinwardly projecting fin 87 of the tube 81 is adjacent the inwardlyprojecting fin 82 of the tube 80. Thus, the fins 84, 85,86 and 87constitute struts interconnecting the inner and outer tubes 80 and 81,maintaining the inner tube in properly centered relation in the outertube, and also constituting both heat conducting elements extendingbetween the inner and outer tubes as well as means defining fourcircumferentially separated axially extending passages 91, 92, 93 and94.

In FIGURE 15 there is shown a similar arrangement which differs only inthat the inner and outer tubes 95 and 96 are each provided with tworadially inwardly projecting fins 97 and 98 respectively and fourradially outwardly projecting fins 99 and 100 respectively.

While FIGURES 14 and 15 show both the inner and outer tubes providedwith fins, it will of course be apparent that either of the tubes may beplain, and only one provided with fins.

The double wall tubing may be constructed by first shaping the outertube to its tubular form, thereafter inser'ting the inner tube in foldedand flattened form, and subsequently expanding the inner tube by fluidpressure or otherwise into the final position.

Alternatively, both inner and outer tubes may be brought to tubularcondition after which they may be assembled together in approximatelyconcentric relation. Thereafter, force may be applied to the innersurface of the inner tube by fluid pressure or otherwise, expanding theinner tube so as to bring about positive firm metal to metal contactbetween the free edges of the fins extending between the inner and outertubes.

The drawings and foregoing specification constitute a description of theimproved tubing having a plurality of inwardly and/or outwardlyextending axial fins and the method of producing the same in such' full,clear, concise and exact terms as to enable any person skilled in theart to practice the invention, the scope of which is indicated by theappended claims.

What I claim as my invention is:

l. The method of making double walled tube struc ture which comprisesflattening and folding a first tubular stock, rolling the flattened andfolded stock to reduce wall thickness and to elongate the stock, andthereafter opening the rolled stock to form a first thin walled tubehaving at least one longitudinally and radially inwardly extendingintegral fin; flattening a second tubular stock of slightly smallertransverse dimensions than said first tubular stock, rolling the secondtubular stock to reduce wall thickness and to elongate the stock;inserting the rolled second tubular stock into the first thin walledtube, and thereafter opening the second rolled tubular stock to form asecond thin walled tube disposed within said first tube and having atleast a pair of longitudinally and radially outwardly extending fins,the fins of both of said tube cooperating to space the second inner tubefrom the first outer tube.

2. The method of making double walled tubing which comprises flatteningand folding tubular stock in such a way as to provide at least threeoutwardly folded creases, rolling the stock to reduce its wall thicknessand to elongate stock, inserting the rolled stock in a tubular member,and opening the rolled stock to form an inner tube having at least threelongitudinally and radially outwardly extending positioning fins,spacing the inner tube from said tubular member.

3. The method of making double walled tubing which comprises flatteningand folding tubular stock in such a way as to provide at least threeoutwardly folded creases, rolling the stock to reduce its wall thicknessand to elongate the stock, inserting the rolled stock in a tubularmember of predetermined size, and opening the rolled stock to form aninner tube having at least three longitudinally and radially outwardlyextending positioning fins dimensioned to engage the inner surface ofsaid tubular member, spacing the inner tube from said tubular memher.

4. The method of making double walled tubing which comprises flatteningand folding tubular stock in such a way as to provide at least threeoutwardly folded creases, rolling the stock to reduce its wall thicknessand to clon gate the stock, inserting the rolled stock in a tubularmember of predetermined size, opening the rolled stock to form an innertube having at least three longitudinally and radially outwardlyextending positioning fins dimensioned to engage the inner surface ofsaid tubular member, spacing the inner tube from said tubular member,and applying internal pressure to said inner tube to expand the same toprovide firm metal to metal contact between the fins of said inner tubeand said tubular member.

5. The method of making double walled tubing which comprises folding andflattening a metal inner tube to cause it to have a cross-sectionalshape such that in folded and flattened condition it can be insertedwithin an outertube having an internal diameter no greater than theexternal diameter of the opened up inner tube, rolling the inner tube ina direction to increase its length without. appreciably increasing itsinternal diameter thereby reducing the wall thickness of the inner tubeand producing both internal and external rib-forming portions, insertingthe elongated flattened folded inner tube into the outer tube, openingup the inner tube into contact with the inner surface of the outer tubeby the application of internal pressure therein, and selecting thedimensions of the tubes such that when the inner tube is fully opened upthe contact between the inner and outer tubes is limited to the outeredges of the outer ribs on said inner tube.

6. The method of making double-walled tube structure which comprisesproviding an outer tube, inserting a collapsed inner tube within saidouter tube, both of said tubes having integral radial fin-formingprojections extending toward the other of said tubes, and opening upsaid inner tube by the application of internal pressure to produce firmcontact between the free edges of the fins formed on one tube with theadjacent surfaces of the other tube, and to thereby radially separatethe tubes in the regions of said fins.

7. The method of making double-walled tube structure which comprisesproviding an outer tube, inserting a collapsed inner tube within saidouter tube, at least one of said tubes having integral radialfin-forming projections extending towards the other of said tubes, andopening up said inner tube by the application of internal pressure toproduce firm contact between the free edges of the fins formed on onetube with the adjacent surface of the other tube, and to therebyradially separate the tubes in the regions of said fins.

8. The method as described in claim 7, wherein the collapsed inner tubehas integral therewith said fin-forming projections.

9. A method of making a double-walled tube comprising the steps ofproducing a combination consisting of an outer tube, and a ribbon in theform of a collapsed inner tube inside the outer tube and having anopening defining the inner periphery of the inner tube when said ribbonis inflated, and having also side marginal sections integral therewithand extending laterally of the ribbon beyond said opening, the lateralwidth of said marginal sections being greater than the thickness of thetube Walls in the ribbon between said marginal sections, whereby saidmarginal sections form outer fins when said ribbon is inflated, andshaping said double-walled tube from said combination into a form inwhich said outer tube is wide open and including the step of inflatingsaid ribbon while in said combinaton to form the inner tube with saidmarginal sections in the form of fins extending between said tubes fromthe outer periphery of said inner tube to the inner periphery of saidouter tube to space said tubes substantially radially in the regions ofsaid fins, the

inner diameter of the outer tube being so related to the outer diameterof the inner tube and to the height of said fins as to cause said finsto extend to the inner surface of said outer tube in firm contacttherewith in shaped condition of said double-walled tube.

10. The method as described in claim 9, wherein said ribbon has foldsdefining internal fins when said ribbon is inflated.

11. A method of making a double-walled tube comprising flattening andfolding a metal inner tube With sufficient folds to form a ribbon havinga width substantially less than the width said inner tube would have ifsaid inner tube were merely flattened to bring the two opposite halvesof the inner tube in face to face contact, said ribbon also having anopening defining the inner periphery of the inner tube when inflated andtwo fin-forming side marginal sections extending laterally of the ribbonbeyond said opening, rolling the flattened, folded ribbon in a directionto reduce the thickness of the walls of the inner tube While maintainingthe lateral widths of said fin-forming sections greater than thethickness of said Walls, said fin-forming sections being located todefine diametrically opposite fins upon inflation of said inner tube,inserting the rolled, flattened, folded inner tube into an outer tube,and inflating the inner tube inside said outer tube by the applicationof internal pressure therein to form an opened up inner tube withdiametrically opposite fins extending radially outwardly therefrom, andspacing said tubes in the regions of said fins, the internal diameter ofthe outer tube being so related to the transverse dimensions of therolled, flattened, folded inner tube as to permit said rolled,flattened, folded inner tube to be inserted into said outer tube andbeing so related to the external diameter of the inner tube and to theheight of said fins when inflated as to cause said fins to firmlycontact the inner surface of the outer tube.

References Cited by the Examiner UNITED STATES PATENTS 167,688 9/75Pufi'er 29421 813,918 2/06 Schmitz 138-62 X 904,189 11/08 Everson 29-5232,001,643 5/35 Wilcox 29534 2,132,565 10/38 Graham 29523 2,611,585 9/52Boling. 2,633,414 3/53 Boivinet 29523 2,643,027 6/53 Fink 13853 X2,780,000 2/57 Huet 29534 FOREIGN PATENTS 190,585 12/22 Great Britain.

WHITMORE A. WILTZ, Primary Examiner. EDWARD V. BENHAM, Examiner.

1. THE METHOD OF MAKING DOUBLE WALLED TUBE STRUCTURE WHICH COMPRISESFLATTENING AND FOLDING A FIRST TUBULAR STOCK, ROLLING THE FLATTENED ANDFOLDED STOCK TO REDUCE WALL THICKNESS AND TO ELONGATE THE STOCK, ANDTHEREAFTER OPENING THE ROLLED STOCK TO FORM A FIRST THIN WALLED TUBEHAVING AT LEAST ONE LONGITUDINALLY AND RADIALLY INWARDLY EXTENDINGINTEGRAL FIN; FLATTENING A SECOND TUBULAR STOCK OF SLIGHTLY SMALLERTRANSVERSE DIMENSIONS THAN SAID FIRST TUBULAR STOCK, ROLLING THE SECONDTUBULAR STOCK TO REDUCE WALL THICKNESS AND TO ELONGATE THE STOCK;INSERTING THE ROLLED SECOND TUBULAR STOCK THE FIRST THIN WALLED TUBE,AND THEREAFTER OPENING THE SECOND ROLLED TUBULAR STOCK TO FORM A SECONDTHIN WALLED TUBE DISPOSED WITHIN SAID FIRST TUBE AND HAVING AT LEAST APAIR OF LONGITUDINALLY AND RADIALLY OUTWARDLY EXTENDING FINS, THE FINSOF BOTH OF SAID TUBE COOPERATING TO SPACE THE SECOND INNER TUBE FROM THEFIRST OUTER TUBE.